The present invention relates to the cooling of components in an electrical machine. In particular the invention relates to apparatus for controlling the flow of a coolant so as to provide generally even cooling of a portion of an electrical machine.
As the demand for electrical power in vehicles has increased, the trend in alternator (generator) design has been toward greater power capacity. At the same time there has been a requirement to make the alternator housing more compact, such that it takes up less space in the vehicle's engine bay. The result of these requirements has been an increased demand on the alternator's cooling system, which must remove the heat generated by the stator/rotor windings which are located in the alternator housing.
An alternator cooling system typically comprises a housing including one or more passages through which a liquid coolant flows. The coolant is usually diverted to the alternator from the vehicle's engine. U.S. Pat. No. 6,633,098 describes an arrangement for cooling the stator and rotor (including windings on the rotor) in a high-output alternator. The stator is supported by brackets which constitute a sleeve structure. Coolant passages run axially along the sleeve and circumferentially at its ends. Coolant enters at one end of the sleeve and follows a circuit which takes it to the other end and back again. It then exits the sleeve, having cooled the stator. The rotor is cooled by a centrifugal fan. Fins and guides are provided for directing the flow of air from the fan.
U.S. Pat. No. 6,046,520 is also concerned with cooling a high-output alternator. A pot-like shell (essentially a tube with a base) is attached to the alternator housing, forming a gap between the alternator housing and the shell. This gap extends circumferentially around, and axially along, the housing. Coolant enters the gap at an inlet which is tangential to the shell. It passes along the gap around the circumference of the shell and exits from an outlet about 300 degrees around from the inlet. The gap between the inlet and outlet (60 degrees apart) is partially blocked to resist the fluid taking the shorter route to the outlet. The inlet and outlet are axially displaced (staggered along the length of the shell) to enhance cooling. There is a restriction about 180 degrees around the circumference of the shell. This restriction causes some of the liquid to be diverted axially to the base area of the shell, where it can cool the bearing in that area. The rest of the liquid passes through the restriction and onto the outlet.
Thus, general arrangements of coolant passages for alternators are known. However, a growing need for the reduction of fuel consumption by the internal combustion engine has led to the development of the Integrated Starter Generator (ISG), which represents an alternative to the conventional alternator. Like an alternator, the ISG generates electric power when the engine is running, for supplying the vehicle's electrical system and charging its battery. However, the ISG combines the functions of the conventional alternator/generator with those of the starter motor in a single ISG. Thus, it is capable of switching from an alternator mode to a starter mode. The ISG can automatically stop and then rapidly restart the engine to avoid periods of unnecessary engine idling, such as when a vehicle is waiting at a traffic light. This reduces fuel consumption and exhaust emissions.
Like an alternator, the ISG includes a stator and rotor which need to be cooled. However, the dual function of the ISG described above means that it requires other components in addition to those usually found in an alternator. In particular, the ISG includes various electrical components for producing the high current needed for starting the engine. Furthermore, complex electronics are necessary to control efficiently the start-stop function of the ISG. Moreover, the ISG faces the same requirement for compactness as the conventional alternator, hence the electrical and electronic components should be integrated into the housing of the ISG in the smallest possible volume. This combination of high-power components in a small, enclosed space means that the ISG generates a large quantity of heat—significantly greater than that of a conventional alternator—which must be efficiently removed in order for the ISG to operate effectively.